Gold hoarded by person who believes speculator (8)
I believe the answer is:
theorist
'speculator' is the definition.
(I've seen this before)
'gold hoarded by person who believes' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'hoarded by' is an insertion indicator (hoard can mean to hold onto).
'person who believes' becomes 'theist' (someone who believes in a god).
'or' placed within 'theist' is 'THEORIST'.
(Other definitions for theorist that I've seen before include "Speculator" , "Expert in established hypotheses" , "Thinker" , "An expert in abstract principles" , "Abstract reasoner" .)